Hierarchical Access Control is a significant and conventional problem in information security. This book deals with an adaptive protocol called Dual Encryption. It uses symmetric polynomials (SP) and group Diffie-Hellman schemes. In this book, detailed study on the various cryptographic schemes for HAC and security issues in HAC have been discussed elaborately. Performance analysis and suitability of the different Diffie - Hellman schemes when combined with the symmetric polynomial scheme for providing hierarchical access control and Security analysis of the DEHAC with the different combinations of contributory key management scheme is also discussed in detail.